Why will my mobile network work on my new phone

Why do I get no mobile service or no cell messages it say no mobile network I have talked with tech support twice for hours of waiting no help. This a a new phone. I reset it back to the factory settings nothing. Pulled the sims card in and out q help. It worked for one week and then nothing. The wifi and such works. It over 30 day warranty. Does anyone no what is wrong. PS it has a non removable battery any help is appreciated! They did say they would make out a certificate for a new sims card but not sure that will fix it. I can't afford to go buy another phone this was a Xmas gift

If a new SIM card doesn't solve the problem, follow the directions in the manufacturer's warranty statement as to what you have to do to make a claim for a manufacturer's warranty repair or replacement. (Ensure that you can get hold of the sales receipt or proof of purchase document for the phone. Whoever gave it to you as a Xmas present may have to make the warranty claim on your behalf, if the receipt was on a credit card rather than a cash sale, where you should be able to make the claim)

(Have you got a friend who has a phone that works on the same network as yours did? If so, ask them if you can try their SIM card in your phone, just to prove whether the problem is the SIM card or not.)

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